All stone-fruits suffer more or less from an excessive flow of gum. The name gummosis[67] is generally applied to these troubles. Gumming is much more prevalent in the far West than in the East but is to be found wherever stone-fruits are grown. This excessive gumming is a secondary effect of injuries caused by fungi, bacteria, insects, frost, sunscald, and mechanical agencies. There is a good deal of difference in the susceptibilities of varieties and species to this trouble, the Sweet Cherry suffering much more than the Sour sorts and varieties of other species having hard wood suffering less than those having softer wood. There is less gummosis, too, on trees in soils favoring the maturity of wood; under conditions where sun and frost are not injurious; and, obviously, in orchards where by good care the primary causes of the diseases are kept out. A number of diseases of the trunk arise from mechanical injuries from wind, sun, frost and hail. Few, indeed, are the fruit-growers whose trees are not occasionally damaged in one way or another in the vicissitudes of a trying climate. Very often these mechanical injuries are followed by fungal parasites or insects so as to make it difficult to distinguish the primary from the secondary trouble. There is a wide difference in the susceptibility of _Prunus avium_ and _Prunus cerasus_ to such injuries, the Sweet Cherry, with its softer wood, being much more easily injured by any and all stresses of weather than the Sour Cherry. In the main the elements cannot be combated but low heading of the trees is a preventive from sunscald, at least, and sometimes may have a favorable effect in preventing wind and frost injuries. [55] Smith, E. F. Peach Rot and Peach Blight, _Journ. Myc._ =5=:123-134. 1889. Quaintance, A. L. The Brown Rot, etc., _Ga. Sta. Bul._ =50=:237-269, figs. 1-9. 1900. [56] Farlow, W. G. The Black Knot, _Bulletin Bussey Institution_ 440-453. 1876. Halsted, B. D. Destroy the Black Knot, etc., _N. J. Sta. Bul._ =78=:1-14. 1891. [57] Duggar, B. M. _Fungous Diseases of Plants_ 185, fig. 68. 1909. [58] Higgins, B. B. Contributions to the Life History and Physiology of Cylindrosporium on Stone Fruits, _Am. Jour. Bot._ =1=:145-173. 1914. [59] Aderhold, R. Mycosphaerella cerasella n. spec., die Perithecienform von Cercospora cerasella Sacc. und ihre Entwicklung, _Ber. d. deut. bot. Ges._ =18=:246-249. 1900. [60] Duggar, B. M. _Fungous Diseases of Plants_ 314. 1909. Pierce, N. B. A Disease of Almond Trees, _Jour. Myc._ =7=:66-67, Pls. 11-14. 1892. [61] Duggar, B. M. _Fungous Diseases of Plants_ 226. 1909. [62] Smith, E. F. and Townsend, C. O. A Plant Tumor of Bacterial Origin, _Science_ =25=:671-673. 1907. Toumey, J. W. Cause and Nature of Crown Gall, _Ariz. Sta. Bul._ =33=:1-64, figs. 1-31. 1900. Hedgcock, G. C. Crown Gall, etc., _U. S. Dept. Agr. Bur. Pl. Ind. Bul._ =90=:15-17, Pls. 3-5. 1906.